Process for the purification of the waste gases from the liquid-phase oxidation of cyclododecane



United States Patent 3,324,189 PROCESS FOR THE PURIFICATION OF THE WASTE GASES FROM THE LIQUID-PHASE OXIDATION OF CYCLODODECANE Horst Grasemann, Marl, Germany, assignor to Chemische Werke Huls Aktiengesellschaft, Mar], Germany No Drawing. Filed Jan. 26, 1965, Ser. No. 428,235 Claims priority, application Germany, Mar. 24, 1964, C 32,489 7 Claims. (Cl. 260-666) The present invention relates to the purification of gases resulting from the liquid phase oxidation of cyclododecane. More particularly, it relates to the purification of said gases by treatment with cyclododecatriene at temperatures below 65 C., followed by hydrogenation of the water-washed cyclododecatriene-cyclododecane mixture.

The liquid phase oxidation of aliphatic and cycloaliphatic hydrocarbons with oxygen and oxygen-containing gases is well known. In carrying out the process, the exhaust gases from the process contain valuable components which must be recovered in order to make the process economical. The composition of these exhaust gases varies both with the reactants and the operating conditions. Generally, they consist mainly of non-oxidized hydrocarbons either alone or mixtures thereof, acid products such as formic or acetic acids, carbon dioxide, and water. These products can be removed in part from the exhaust gases by cooling and condensation and the unoxidized hydrocarbons returned to the oxidation system after intermediate treatment or purification.

While the above described procedure is suitable for the oxidation of certain hydrocarbons, it is entirely unsatisfactory for some hydrocarbons such as cyclododecane, which melts at 61 C. In attempting to apply the above procedure to the process of liquid phase oxidation of cyclododecane with oxygen or oxygen-containing gases, the cyclododecane condenses as a solid in the condensers and chokes up the cooling system at the customary cooling temperatures. In order to attempt to overcome such difficulties it has been suggested that the cooling temperature be maintained at approximately 60 C. and that the greater portion of the unreacted molten cyclododecane be returned to the reactor, and then to subject the remaining exhaust gases which have been freed from the unreacted cyclododecane to further cooling in a crystal separator. Such a process, however has proven unsatisfactory because the cooling surface of the separator becomes so highly insulated by the separated cyclododecane that subsequent gaseous currents of exhaust gases from the oxidation system will pass therethrough without any effective purification. Further purification of the exhausts gases can then only be accomplished by the frequent and expensive reversals of the crystal separators for successive cooling (and condensation of the cyclododecane) and melting of the condensed cyclododecane.

Attempts have also been made to effect satisfactory separation of the exhaust gases by first cooling the gases to approximately 65 C. and then passing them through a heavy oil in which the entrained cyclododecane is soluble. This procedure, however, has proven unsatisfactory because of the fact that the heavy oil required by the high boiling point of the cyclododecane (122 C. at 20 torr) necessitates the use of expensive distillation equipment and operations for the separation of the cyclododecane in a form so that it can be reused in the oxidation process.

It has now been discovered, according to the present invention, that the unoxidized cyclododecane can be economically recovered from the exhaust gases from the liquid phase oxidation of cyclododecane with oxygen or oxygen-containing gases in a form suitable for reuse in the oxidation process by subjecting the said exhaust gases to a preliminary cooling to about 65 C., followed by washing the cooled gases with cyclododecatriene, washing the resulting cyclododecatriene-cyclododecane mixture with water (or dilute aqueous alkaline solutions), and then subjecting the washed mixture to hydrogenation. The hydrogenated product can then be returned to the oxidation process where it can be satisfactorily oxidized. In this manner, satifactory yields of the desired oxidation products can be obtained in an economical manner.

In carrying out such a process, cyclododecane is subjectcd, in accordance with procedures well-known in the art, to liquid phase oxidation with oxygen or oxygencontaining gases under 1 atmosphere pressure and at temperatures of the order of -180 C., and preferably between and C. In such a process, the exhaust gases from the reactor are generally at temperatures between 130 and C., and preferably between 145 and 165 C. When oxygen is used as the oxidizing medium, the exhaust gases usually contain approximately 85-95% by volume of nitrogen, 4-6% by volume of oxygen, 12% by volume of hydrogen, and 1% by volume of carbon dioxide. With the exhaust gas at 160 C. and

under a corresponding stream pressure one cubic meter of the exhaust gas contains approximately 0.88 kg. of cyclododecane. By passing the exhaust gas of such composition through a conventional type cooler wherein it is reduced to a temperature of 65 C., 85 to 95% of its cyclododecane content is removed.

The residual gas from which the cyclododecane has been partially removed is next conducted to the bottom of a cooling tower, preferably, filled with raschig rings or other suitable filling material. The residual gas passing up through this tower comes in contact with cyclododecatriene introduced preferably in the form of a spray into the top of the tower. If desired, cyclododecatriene can be circulated from the bottom of the column until saturated with absorbed cyclododecane, and a portion thereof then removed continuously as an equivalent amount of fresh cyclododecatriene is added to replace the saturated cyclododecatriene removed.

The temperature in the cooling tower is maintained Within the range of 1040 C., and preferably within the range of 10-20 C., by cooling the circulating cyclododecatriene with Water coolers, or other suitable means.

At 10 C. 100 ml. of cyclododecatriene dissolves 32.5

g. of cyclododecane, whereas at 40 C. the same amount dissolves about 100 g.

The cyclododecatriene-cyclododecane mixture from the cooling tower is next washed with cold water, preferably containing 2% by weight of sodium hydroxide or other alkali, to remove the entrained acid components such as formic and acetic acids, which are present in amounts of the order of 1% by weight.

The washed cyclododecatriene-cyclododecane mixture is then hydrogenated !by means well known in the prior art, as for example, under pressures ranging from 250 to 350 atmospheres, and preferably at 280 to 320 atmospheres and at a temperature of the order of 200 C., by the aid of hydrogenation catalysts such as copper-nickelchromiuml catalysts. This hydrogenation converts the cyclododecatriene to cyclododecane so that only the latter remains after separation of the hydrogenated mixture from the catalyst.

The above operation thus permits the recovery in a high state of purity of the unoxidized cyclododecane in the exhaust gases and in a form which can be returned to the oxidation stage first described, or to fresh cyclododecane which is to be oxidized.

The cyclododecatriene used to absorb the cyclododecane from the exhaust gases is surprisingly not oxidized by the oxygen of the exhaust gas, even though it is known that cyclododecatriene can be readily oxidized even at room temperature. For some unexpected and unknown reason the cyclododecatriene is oxidized only to a very slight degree under the conditions of use described above,

The example which follows describes specific operating procedures. It should 'be understood, however, that variations from the specific conditions shown will be obvious to one skilled in the art. Any such variations which do not depart from the concept of the disclosed invention are intended to come within the scope of the appended claims.

Example Percent by volume Nitrogen 89.3 Oxygen 9.0 Hydrogen 0.5

Carbon dioxide 0.5

and 1.5 tons of cyclododecane, which were removed from the reactor at a temperature of 160 C. On passing this exhaust gas through a cooler maintained at a temperature of 65 C. by means of warm water 1400 kg. of cyclododecane were liquefied and removed from the exhaust gases. The remainder of the exhaust gas was then conducted into the bottom of a tower filled with raschig rings, and into the top of which was sprayed cyclododecatriene from a water-cooled closed circulating system which permitted the cyclododecatriene to be kept at any desired temperature. When maintaining the temperature of the exhaust gas at C., the gas leaving the tower was found to be practically free from cyclododecane.

The liquid from the tower, consisting of a mixture of cyclododecatriene and cyclododecane, was then washed with 2% sodium hydroxide solution and hydrogenated at 200 C. under a pressure of 300 atmospheres in the presence of a conventional copper-nickel-chromium hydrogenation catalyst, whereby the cyclododecatriene was substantially completely converted into cyclododecane. The hydrogenated mixture was found to be satisfactorily oxidizable when returned to the first stage of the above 4 described oxidation operation where the cyclododecane was subjected to liquid phase oxidation by oxygen.

What is claimed is:

1. Process for the purification of exhaust gas from the liquid phase oxidation of cyclododecane with oxygen which comprises: cooling said exhaust gas containing cyclododecane to a temperature slightly above the solidification temperature of cyclododecane, separating the condensed cyclododecane, subjecting the resulting gaseous mixture containing residual cyclododecane to scrubbing with liquid cyclododecatriene at temperatures below the solidification temperature of cyclododecane to dissolve the latter in said liquid cyclododecatriene, washing the resulting cyclododecatriene-cycledodecane mixture with a member of the group consisting of water and a dilute aqueous alkaline solution, subjecting the washed cyclododecatriene-cyclododecane mixture to hydrogenation, and recovering the resulting cyclododecane.

2. The process of claim 1 wherein the crude exhaust gas from the oxidation unit is cooled to a temperature of the order of C. to separate the major portion of' the cyclododecane therein.

3. The process of claim 1 wherein the exhaust gas from which the major portion of the cyclododecane has been removed is subjected to scrubbing with liquid cyclododecatriene at temperatures ranging from 10 to 40 C.

4. The process of claim 1 wherein the crude cyclododecatriene cyclododecane mixture is washed with dilute aqueous sodium hydroxide solution.

5. The process of claim 1 wherein the washed cyclododecatriene-cyclododecane mixture is subjected to hydrogenation with a nickel-copper chromium catalyst at pressures ranging from 250 to 350 atmospheres and at a temperature of the order of 200 C.

6. In a process for the purification of a gas containing cyclododecane, the step which comprises scrubbing said gas with liquid cyclododecatriene at a temperature below the solidification temperature of cyclododecane to dissolve said cyclododecane in said cyclododecatriene.

7. A process as defined by claim 6, comprising a further step of washing resultant cyclododecatriene-cyclododecane solution with a member of the group consisting of water and a dilute aqueous alkaline solution.

References Cited UNITED STATES PATENTS 3,022,359 2/1962 Wiese et al. 260-666 3,109,860 11/1963 Lidor et al. 260-666 DELBERT E. GANTZ, Primary Examiner.

V. OKEEFE, Assistant Examiner. 

1. PROCESS FOR THE PURIFICATION OF EXHAUST GAS FROM THE LIQUID PHASE OXIDATION OF CYCLODODECANE WITH OXYGEN WHICH COMPRISES: COOLING SAID EXHAUST GAS CONTAINING CYCLODOECANE TO A TEMPERATURE SLIGHTLY ABOVE THE SOLIDIFICATION TEMPERATURE OF CYCLODODECANE, SEPARATING THE CONDENSED CYCLODODECANE, SUBJECTING THE RESULTING GASEOUS MIXTURE CONTAINING RESIDUAL CYCLODODECANE TO SCRUBBING WITH LIQUID CYCLODODECATRIENE AT TEMPERATURES BELOW THE SOLIDIFICATION TEMPERATURE OF CYLCLODODECANE TO DISSOLVE THE LATTER IN SAID LIQUID CYCLODOECATRIENE, WASHING THE RESULTING CYCLODODECATRIENE-CYCLODODECANE MIXTURE WITH A MEMBER OF THE GROUP CONSISTING OF WATER AND A DILUTE AQUEOUS ALKALINE SOLUTION, SUBJECTING THE WASHED CYCLODODECATRIENT-CYCLODODECANE MIXTURE TO HYDROGENATION, AND RECOVERING THE RESULTING CYCLODODECANE. 